1. Field of the Invention
This invention relates to the preparation of ethers and, more particularly, to the preparation of methyl tertiary-butyl ether.
2. Description of the Prior Art
Methyl tertiary-butyl ether (MTBE) is a high-octane blending agent for motor fuels and can have a blending Research Octane Number (RON) of over 120 in lead-free gasoline. The considerable interest taken in MTBE and processes for its economical large scale manufacture is evident in the many patent and literature references which relate to this compound (see, for example, U.S. Pat. Nos. 1,968,601; 2,067,385; 2,197,023; 2,282,469; 2,391,084; 2,480,940; 2,544,392; 2,805,260; 2,853,331; 3,135,807; 3,718,701; 3,726,942; 3,821,315; 3,825,603; 3,846,088; 3,849,082; and, 4,148,695; Belgian Pat. Nos. 612,388; 829,299; 829,300; and 829,303; British Pat. No. 1,272,585; and, German Pat. Nos. 2,246,004 and 2,521,963 among others). Many proposals for making MTBE are based on the catalyzed reaction of isobutylene with methanol. According to U.S. Pat. No. 2,805,260, this reaction can be catalyzed by boric acid and inorganic complexes of heteropoly acids. In U.S. Pat. No. 3,135,807, the catalyst of choice is bismuth molybdate or a lead, antimony, tin, iron, cerium, bismuth, nickel, cobalt or thorium salt of phosphomolybdic acid optionally supported on an inert carrier. U.S. Pat. No. 3,821,315 discloses still other molybdenum-containing catalysts. One widely studied catalyst is based on a cation exchange resin such as divinyl benzene cross-linked polystyrene cation exchange resin in which the active sites are sulfuric acid groups (viz, U.S. Pat. Nos. 3,726,942; 3,821,315; 3,846,088; and 3,849,082; and, German Pat. Nos. 2,629,769; 2,646,333; and 2,752,111). Polish Pat. No. 103,379 discloses the preparation of MTBE from methanol and isobutylene over zeolite X or Y which was largely dealuminized and cation exchanged.